It has been well known that in order to generate electricity with good efficiency with a solid polymer fuel cell, it is desirable that the electrolyte membrane be in an adequate humidified state and that no excess moisture be present inside the fuel cell. The technique described, for example, in Patent Document 1 is known for controlling the amount of moisture in the cell plane of the fuel cell. Patent Document 1 discloses the feature of adjusting at least one of pressure, humidity, flow rate, and pressure loss characteristic determined by the flow channel shape for a reaction gas (a general term for an oxidizing gas such as air and a fuel gas such as hydrogen gas) to control the distribution of moisture amount as water vapor or liquid droplets in the cell plane. Patent Documents 2 to 5 are other prior art documents.    Patent Document 1: Japanese Patent Application Publication No. 2004-335444    Patent Document 2: Japanese Patent Application Publication No. 2005-222854    Patent Document 3: Japanese Patent Application Publication No. 2009-004151    Patent Document 4: Japanese Patent Application Publication No. 2008-041505    Patent Document 5: Japanese Patent Application Publication No. 2005-339845
However, in an actual fuel cell, a large number of unit cells are stacked, the moisture amount differs along the stacking direction and the moisture amount also differs in the flow channel direction of the reaction gas flow channel in the cell plane. In this regard, in the configuration described in Patent Document 1, the moisture amount in the stacking direction of fuel cells or moisture amount in the flow channel direction of the reaction gas flow channel are not taken into account in the control process and the distribution of moisture amount inside the fuel cell is difficult to control with good accuracy.
Due to the increase in fuel consumption in recent years, the number of fuel cell systems in which intermittent operation of fuel cells is performed has increased. In the intermittent operation, the operation of an auxiliary device that supplies the reaction gases to the anode electrode and cathode electrode is stopped.
However, during the operation stop in intermittent operation, an excess amount of water vapor or nitrogen gas can remain as impurity inside the fuel cell. In such case, when the operation is thereafter started, the supply of reaction gases can be insufficient, the cell voltage can decrease, and fuel consumption can increase under the effect of the remaining water vapor or nitrogen gas.